Definition: 1.11: Obtuse Angle
An obtuse angle is one greater than a right angle.
Modern Definition
Euclid's definition corresponds to today's formulation.
Example
The angle \(\angle{RQP}\) (marked light-green) is obtuse.
![angle](https://github.com/bookofproofs/bookofproofs.github.io/blob/main/_sources/_assets/images/examples/angle.jpg?raw=true)
In the following figure both angles \(\angle{ABC}\) and \(\angle{CBA}\) are obtuse.
![Fig5p0p1](https://github.com/bookofproofs/bookofproofs.github.io/blob/main/_sources/_assets/images/examples/Fig5p0p1.jpg?raw=true)
Mentioned in:
Axioms: 1
Definitions: 2 3 4
Proofs: 5 6 7
Propositions: 8 9 10
Thank you to the contributors under CC BY-SA 4.0!
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References
Adapted from CC BY-SA 3.0 Sources:
- Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014
Adapted from (Public Domain)
- Casey, John: "The First Six Books of the Elements of Euclid"
Adapted from (subject to copyright, with kind permission)
- Fitzpatrick, Richard: Euclid's "Elements of Geometry"